Picolinic acid is a metabolite of the tryptophan catabolism. Picolinic acid is produced under inflammatory conditions and a costimulus with interferon-gamma (IFNgamma) of macrophage (Mphi) effector functions, is a selective inducer of the Mphi inflammatory protein-1alpha (MIP-1alpha) and -1beta (MIPs), two chemokines/cytokines involved in the elicitation of the inflammatory reactions and in the development of the Th1 responses. IFNgamma and picolinic acid have reciprocal effects on the production of MIPs chemokines and the expression of their receptor. The concerted action of IFNgamma and picolinic acid on MIP-1alpha/beta chemokine/receptor system is likely to be of pathophysiological significance and to represent an important regulatory mechanism for leukocyte recruitment and distribution into damaged tissues during inflammatory responses. Picolinic acid has an effect on the production of L-arginine-derived reactive nitrogen intermediates in macrophages, by augmenting IFN-gamma-induced NO2- production, and acts synergistically with IFN-gamma in activating macrophages. Children with acrodermatitis enteropathica (AE) are treated with oral zinc dipicolinate (zinc-PA). The concentration of picolinic acid in the plasma of asymptomatic children with AE was significantly less than that of normal children. However, oral treatment with PA alone is ineffective. The results support the hypothesis that the genetic defect in AE is in the tryptophan pathway, although the role of PA in zinc metabolism remains to be defined.